1. Field of the Invention
The present invention relates to the field of projection screens, and more particularly, to projection screens utilized in front projection composite photography.
2. Art Background
Composite photography is the art of combining two or more separately photographed subjects into one scene. In motion picture production, a classic example of this technique is the rendition of a scene comprising an automobile interior inhabited by actors with an exterior street scene visible through the automobile windows. Other examples of composite photography include the placement of fictional objects, such as futuristic spacecraft or extraterrestrial landscapes, in a scene with live actors or full scale props.
Front projection is a method of composite photography which was originally developed through the work of Walter Thorner around 1932, as part of an effort to overcome the shortcomings inherent in rear projection processes. In a typical front projection system, a camera and projector are disposed at substantially 90.degree. with respect to one another, and a partially silvered mirror is located at an approximate B 45.degree. angle relative to both the camera and projector (see FIG. 1). The projector projects an image onto a background screen disposed in back of a foreground object. The camera then photographs both the projected background scene as well as the foreground object on one or more frames of film.
It was soon realized that a major requirement of the front projection screen was to return the projected image back to the camera lens as efficiently and as uniformly as possible. The optical path of the projected image must be substantially coincident with the path of the return images seen and recorded by the camera. In early front projection systems, the background scene failed to equal the foreground scene in image quality. This degradation of the projected image threatened to destroy the illusion created by the front projection process.
In 1951, the Motion Picture Research Council, Inc. issued Report No. 58.334-D by Herbert Meyer, Chief chemist, entitled: "Front Projection Process Photography with Scotchlite". This report described the optical qualities of a material referred to as "Scotchlite" and its application to photographic front projection. This reflective material had been developed by Philip Palmquist and manufactured by the Minnesota Mining and Manufacturing Company ("3M"). Scotchlite material is the subject of two issued U.S. patents: U.S. Pat. No. 2,294,930, dated Sept. 8, 1942 and U.S. Pat. No. 2,379,741, dated July 3, 1945. Scotchlite was originally intended for traffic signs and the like and included minute glass beads, each of which acted like a concave mirror, reflecting back, not the whole projected image, but rather, a small portion of the image.
The 1951 report by Herbert Meyer delineated in a very methodical fashion the various ways in which Scotchlite might be expected to have utility in motion picture production. Meyer examined the effects of camera movements by dollying, panning, tilting, etc., and concluded that, while movements that called for the camera to pivot about the nodal point of its lens, as in panning and tilting, were permissible, the system should otherwise be regarded as a stationary camera system. In his conclusion, Meyer stated that "[t]he fabricating of a large size screen from Scotchlite materials will introduce the problem of seams, which may require special attention".
In the intervening years, it has been found that Scotchlite seams have presented a significant problem in sophisticated front projection composite photography. The manufacturer of Scotchlite, initially advised that it would be sufficient to lay the material out in strips horizontally, and as long as necessary, in a shingle fashion, with each succeeding layer overlapping the previous one. Another method described "butt joints" with a half inch wide Scotchlite strip covering the joint. However, it was soon apparent that the problem of seams in front projection systems utilizing a Scotchlite screen was much more complex than merely disguising the seam itself. As a result of the rather critical nature of the optics involved, and the vagaries of the mass production process, there were preceptible differences in the Scotchlite material, even within the same roll. The material had not only to be joined together, but first broken up into relatively small pieces and "shuffled" in order to reassemble it as a mosaic and thereby produce a homogenous whole onto which an image could be projected.
Various methods were employed to accomplish the homogenizing of a Scotchlite screen. Cutting the material into squares, while economical, left a checkerboard pattern that was readily discerned by an audiences' eyes used to identifying straight lines and right angles. Tearing the Scotchlite material into irregular patches and placing it on a screen was found to be an improvement, but highly labor intensive and wasteful of material. Some improvement was obtained by cutting the Scotchlite material into hexagons, thus reducing the number of conjoint segments and limiting the length of a single edge. However, even through the use of hexagons, there were still straight lines evident, and a solution was required that would eliminate the straight line phenomena without incurring a waste of material.
As will be described, the present invention overcomes the historic problems associated with utilizing Scotchlite or other high gain screen materials in a front projection system. The present invention provides a screen, having particular utility in front projection composite photographic systems, comprised of a plurality of uniquely formed complementary sections of high gain screen material. As will be appreciated from the discussion which follows, although the present invention is particularly suited for use with Scotchlite type materials, it may be used in numerous applications which require a homogenous projection screen.